1. Technical Field
The present invention generally relates to structure foundations and in particular to pilings that are utilized to support the foundations. Still more particularly, the present invention relates to segmented pilings.
2. Description of the Related Art
Many structures have been built on foundations or slabs made of concrete poured on top of soil. Constant changes in the weather and moisture levels in the soil frequently cause damage to such a foundation. In many instances, the foundation may buckle or even crack. This phenomenon occurs for a variety of reasons, including uneven changes in the water content of supporting soils, uneven compacting of soils, and uneven loads being placed on soils. Over time, uneven movement in the soils under a foundation can cause a foundation to bend or crack.
There are several methods used in repairing foundations. One of the most effective and widely used methods includes the use of one or more piles driven into the soil beneath a foundation to form one or more supports. Most of the supports are made primarily of concrete and have an overall cylindrical shape with length and diameter varying according to the soil type and the weight of the structure. For clarity, the words xe2x80x9cpiling sectionxe2x80x9d and xe2x80x9csectionxe2x80x9d signify a single cylindrical piece, and the words xe2x80x9cpilexe2x80x9d and xe2x80x9cpilingxe2x80x9d signify a plurality of sequentially stacked pieces (sections) to form a single support column. A plurality of piles or pilings provide overall load support for a structure in the form of a piling system.
One of the most successful foundation repair procedures involves excavating, or partially excavating, underneath the grade beams that need to be supported or raised, placing a concrete or steel piling section in the excavated cavity underneath the grade beam, placing a construction jack between the grade beam and the piling section, and then operating the jack by hydraulic or pneumatic action to force the piling section downward into the ground while pushing against the bottom of the grade beam. Once the piling section is driven sufficiently into the ground so that its top is flush with the bottom of the excavated area, another piling section is put in place on top of the previous piling section and the jack is reactivated. Eventually, either the piling made up of the piling sections will hit a competent load bearing strata, or the combination of the skin friction between the piling and the ground and the resistance at the end of the piling will make it impossible to the piling any further.
Prior art utilizes piling systems, for foundation support, that are still in use today. For instance U.S. Pat. Nos. 2,645,090 and 3,899,891 describe inventions for assembling segmented pilings on site and then connecting the piling segments to each other with post tensioned cables. Both inventions contemplate tensioning the cable before the piling is driven. U.S. Pat. No. 5,399,055 describes a means for reinforcing a segmented piling, after the piling has been driven into the ground. U.S. Pat. No. 5,288,175 describes a system for driving segmented concrete pilings into the ground while concurrently threading the piling sections onto a cable. After the piling is driven, the cable can be tensioned.
The current art has problems. The sections are strung onto the cable above ground, generally next to the excavation. Threading each piling section onto the cable is labor intensive. Each piling section must be threaded onto the cable and moved along the length of the cable. Enough space must be available to perform the operation. Since cable lengths are typically a minimum of 25 feet, a considerable amount of working room is needed adjacent to the excavation. The ultimate length of the piling is not known before the piling is driven, and the length of precut cable sections will not match the length of the piling. If the cable is too long, material is wasted; if the cable is too short, the piling will not be properly reinforced or tensioned. Piling sections must be small enough for threading along the cable.
When driving a piling section, it is necessary to avoid placing pressure directly on the cable. This is accomplished by using a xe2x80x9cbending templatexe2x80x9d as described by Knight, or by placing a driving ram (used to push a piling into the ground) in an off center position to avoid the cable. Using the xe2x80x9cbending templatexe2x80x9d is labor intensive. Placing the driving ram in an off center position increases the failure rate of piling segments and can cause pilings to deviate from a vertical orientation as they are driven.
Therefore it would be desirable to provide a method and apparatus that would eliminate the specified pre-cut cable lengths for a piling with a plurality of sections. It would also be desirable to eliminate the need for a bending template. It would desirable to provide a cable anchor device that would eliminate the need to thread piling sections on the cable and still provide a positive lock on the end of the cable.
It is therefore one object of the present invention to provide a post-tensioned, segmented, concrete piling.
It is another object of the present invention to utilize a cable for post-tensioning a segmented piling system without the necessity for a bending template.
It is yet another object of the present invention to provide a cable anchor that will provide a positive lock on a cable that is utilized for post-tensioning a segmented piling system, where the cable is installed after the piling is driven.
The foregoing objects are achieved as is now described. The invention comprises a cable anchor as a base segment for multiple concrete piling segments. After installing all the concrete segments on top of the cable anchor, a cable is inserted into passages in the segments to provide post tensioning to the piling. The cable is threaded through the completely installed piling segments and into the cable anchor. After the cable bottoms out in the cable anchor, upward tension is applied to the cable. As the cable is pulled, cable locking members in the cable anchor increase gripping pressure even as the cable tension increases, thereby solidly anchoring the end of the cable in the cable anchor. After the desired tension is reached, the cable is terminated at the top of the last segment. The top end of the cable is then held in place by a termination lug.
The exterior of the cable anchor is a metal cylinder with an end plate on the bottom of the cylinder. Inside the cylinder is an insert that has a bore shaped like the interior of an hourglass with two truncated conical bore sections, wherein the smaller diameters are connected by a cylindrical bore section. The lower truncated conical section is shaped so that two half-conical cable lock members will fit tightly into said conical opening. The portion of the lower conical bore section that is not occupied by the cable lock members is filled with a conical resilient rubber pad.
In the present invention, each cable lock member consists of one half of a cone, where such cone has been split along the long axis of the cone that passes from the tip of the cone through the center of the bottom of the cone. A flat face is formed where the cone is split. A semi-cylindrical groove is cut into the flat face of each half cone such that the groove passes from the tip of the half cone down to the bottom of the half cone. The groove is cut parallel to the long axis of the half cone and passes from the tip of the half cone to the center of the bottom edge of the flat face of the half cone. Teeth are formed in the groove pointing inward to the center of the groove and downward away from the top of the cone.
When pressed together, the two lock members form a cone with a cylindrical opening that passes through the top of the cone, along the vertical axis of the cone, and out through the center of the bottom of the cone.
The upper conical opening in the insert, the cylindrical passage in the center of the insert, the lower conical opening in the insert, the cylindrical opening through the lock members, and a cylindrical opening in the resilient pad are all filled with oil, grease, or other agents designed to protect the end of the cable from corrosion. All the open space in the insert is filled with a rust inhibitor.
A cable is inserted through a channel, conduit, guide, or similar opening, that leads the end of the cable into the top opening of the cable anchor. The sloping sides of the top hollow truncated conical bore section in the insert guide the cable into the cylindrical passage, which connects the top conical bore section to the bottom conical bore section. The cable is then pushed into said cylindrical passage.
The cylindrical passage directs the end of the cable through the lock members into a cavity below the lock members. The two lock member are held in place by the resilient pad. The pad acts as a spring to hold the lock members in place and also allows the lock member to be pushed downward while a cable is being pushed through the cable lock members. The anchor is similar to a finger trap in that the harder the cable is pulled, the more firmly the anchor grips the cable.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.